Neutron flux is typically measured by the effect of interactions between neutrons and their surroundings. For example, neutrons may interact with a material to be detected, and thus create a measurable effect. Detectors may be used to detect such effects, which may include high-energy and ionizing radiations resulting from absorptive reactions, activation processes, and elastic scattering reactions, for example. “High-energy radiation,” as used herein, refers to radiation of neutrons, X-rays, gamma rays, α particles, and β particles.
Detectors of high-energy radiation may include, for example, ion chambers, proportional counters, Geiger-Mueller counters, and scintillation counters. FIG. 1 shows an exemplary prior art detector that may be used to measure hydrogen content by detecting thermal neutrons reflected back from a target. As shown, a basic system 10 for neutron detection includes a target chamber 13, an ion chamber 14, and electronics (not independently illustrated). Fast neutrons 12 are produced by a neutron source 11. These fast neutrons 12 interact with hydrogen nuclei H in the target chamber 13 until their velocity is reduced to the average thermal velocity of the target through a process known as neutron moderation. Specifically, neutron moderation involves a collision and energy transfer from a fast neutron to a target nucleus, wherein the velocity of the fast neutron decreases to that of a slow neutron after the collision and energy transfer. The thermal (slow) neutrons are then scattered from the target chamber 13 to the ion chamber 14.
In the example of a commonly used neutron detector shown in FIG. 1, the ion camber 14 may be filled with a gas (such as He-3) that may interact with the thermalized neutrons to produce ions. When a He-3 atom absorbs (captures) a thermalized neutron, a nuclear reaction occurs and the resultant products are a positively ionized tritium (H-3) atom and a proton. The positively ionized H-3 atoms and protons travel through the gas, pulling electrons in their wake and thus creating an equal number of positive ions and electrons. When a potential is applied across the electrodes 40, 45 in the ion chamber 14, the positive ions are swept to the negatively charged electrode and the electrons are swept to the positively charged electrode, producing currents that are directly proportional to the number of ions transferred. The number of ions transferred depends on the rates of their formation and hence the neutron flux. Thus, the ion currents measured by the ion chamber may be used to derive the magnitudes of the neutron flux, which may be used to determine the amount of hydrogen in the target material.
However, the ion currents generated in these processes are extremely small (on the order of 10−12 amp), making it difficult to accurately determine neutron flux. In addition, temperature and humidity changes in various electronic components, cables, etc. may further compromise the accuracy of the measurements. The situation is even worse under field conditions, which often include wide variations in temperature and humidity.
While prior art high-energy radiation detectors are capable of providing satisfactory measurements, there remains a need for detectors that may provide more reliable and accurate measurements of high-energy radiations.